Aerosol dispensing containers have found widespread use in the packaging of fluid materials including a variety of both liquid and powdered particulate products. Such containers are provided with a valve-controlled discharge orifice and operate by the action of a volatile propellant which is confined within the container together with the product to be dispensed. Because the propellant has an appreciable vapor pressure at room temperature, the product in the closed container is maintained under super-atmospheric pressure.
A typical aerosol unit comprises a hollow cylindrical container which is tightly closed at one end and is provided with an opening at its opposite end for receiving a dispensing valve assembly. A closure, commonly referred to as a mounting cup, serves as the closure for the container and as a support for the valve assembly. Typically, the mounting cup comprises a pedestal portion for mounting the valve unit, a panel portion extending from the pedestal portion, a skirt portion depending from the periphery of the panel, and an annular channel portion extending outwardly from the skirt. When the mounting cup is placed in sealing position on the container, the channel is positioned over the bead surrounding the container opening and the lower portion of the skirt adjacent to the channel is flared or clinched outwardly against the container wall adjacent the bead. To ensure adequate sealing between the closure and the container, the cup is provided with a gasket in the channel, or predominantly in the channel, of the cup.
Heretofore, mounting cup seals have been formed by disposing a so-called "cup" gasket in the channel. This type of gasket has the disadvantage of not being stationary relative to the mounting cup during propellant filling or other valve unit assembly operations with the undesirable consequence that when the mounting cup and container are clinched to effect the seal, the gasket is often disposed at an angled position, and thus, the seal may be less effective.
Another commercial method for disposing the gasket onto the mounting cup consists in forming the gaskets in situ from liquid gasket-forming compositions comprising an elastomer dispersed or dissolved in volatile liquid vehicles, so called "flowed-in" gaskets. In the manufacture of such a gasket, the liquid composition is deposited in the desired configuration in the channel of the cup while the cup is rotated beneath a metering nozzle through which the gasket composition flows. The deposit is then converted into a dry solid sealing mass by expelling the liquid vehicle at elevated temperatures. Though this technique of flowing gaskets into place has received wide commercial acceptance, it suffers from the disadvantages of requiring an elaborate drying operation, wherein the mounting cup must be handled carefully so as to avoid undue upset from the horizontal. Costly recovery apparatus for the expelled liquid also must be provided. In sum, the flowed-in gasket is an expensive step in the formation of the mounting cup. See U.S. Pat. No. 3,342,381 as an example of the "flowed-in" gasket.
Other techniques for disposing a gasket onto the mounting cup are described in U.S. Pat. No. 3,417,177, wherein the gasket seal is made of heat shrinkable material. After placing a band of gasket material having a diameter greater than the outside diameter of the skirt of mounting cup, the cup is heated at a temperature and for a time sufficient to shrink the band into tight frictional engagement with the skirt.
Another similar technique is disclosed in U.S. Pat. No. 3,443,006 ("006"), wherein a band of gasket material is swelled through the use of a suitable swelling agent so as to increase its diameter to fit over the skirt of the mounting cup. Subsequently, the swelling agent is removed from the gasket material so that the band will come into tight frictional engagement with the skirt.
Both the heat shrink and swelling techniques for applying a gasket material to the mounting cup have the disadvantage of being costly and relatively time consuming procedures. Note in U.S. Pat. No. 3,417,177, column 4, lines 27-31, that the positioned bands must be heated to 240.degree. F. for about 2-3 minutes in order to obtain a tight friction fit. In the procedure of the '006 patent, the bands must stand in the swelling liquid for a period of 1/2 to 1 1/2 minutes according to example 2, and then allowed to stand for the drying period. Also, in any mass production utilizing the '006 system, an organic liquid recovery system must be employed.
In U.S. Pat. Nos. 4,546,525 and 4,547,948, a novel gasketed mounting cup system is described, including novel method and apparatus, wherein the gasket material is disposed on the mounting cup in the preferred position for effecting a seal between the mounting cup and the bead of the container; and further wherein the disadvantages associated with the aforementioned techniques of applying the gasket material to the cup are obviated. Also, an apparatus and method is provided wherein gaskets are applied to aerosol mounting cups in an exceptionally rapid and efficient manner to form gasketed-mounting cups having excellent sealing characteristics. In general, the method of invention of the aforesaid U.S. Pat. Nos. 4,546,525 and 4,547,948 comprises passing a tubular sleeve of gasket material onto a compressible mandrel; initially positioning and aligning the skirt of the mounting cup and the contiguous end of the mandrel such that the sleeve of gasket material may pass onto the skirt, said mandrel having fixed and moveable portions with respect to each other and to their movement toward and away from the mounting cup; urging the moveable portion of the gasket material bearing mandrel toward the mounting cup such that the gasket material passes onto the skirt of the cup; causing the moveable portion of the mandrel to retract to its initial position, cutting the sleeve at a point between the mounting cup and the mandrel to leave a band of gasket material; and subsequently, advancing the mounting cup to a station whereat the band of the gasket material is urged further onto the skirt of the mounting cup, whereby, the band of gasket material does not extend beyond the skirt of the mounting cup. Subsequently, the gasket is advanced to the ultimately desired position on the mounting cup.
U.S. Pat. No. 4,559,198 concerns a further refinement of a "sleeve" type gasket system which employs annular (or radial) compressive deformations or "ribs" in the band of gasket material. This ribbing imparts to the gasket a resistance to being dislodged during "under the cup" propellant filling operations. This ribbing also imparts to the gasket a resistance to being repositioned on the mounting cup by the gasket returning to its initial position.
In addition to the type of mounting cup gasket systems described heretofore, namely, "cut", "flowed-in" and "sleeve" gasket, a recent commercial system involves laminating a plastic material to a sheet of the metal and subsequently forming the laminated plastic sheet into a mounting cup. The thickness of the plastic laminate is usually on the order of 0.008-0.010", thinner than the sleeve gasket and substantially thinner than the cut or flowed-in gasket.
This variation in gasket thickness among the several gasket systems, further complicated by the fact that the channel portion of the mounting cups manufactured by the valve assembly plants and the annular beads of the aerosol container manufactured by container plants have nominal variations which are within quality control limits, often produce a defective seal in a completed aerosol product which may remain undetected until ultimately discovered by the consumer.
Recently, attention has been focused on modifications of the shape and configuration of the mounting cup used over the past twenty-five years in the aerosol industry. Such a modification is described in U.S. Pat. No. 4,792,067. This modification of the mounting cup comprises a channel portion for sealing with the bead of the container, the channel portion having an inner region contour being substantially different in shape from the inner surface contour of the annular bead of the container. The difference in the shape of the inner region contour of the channel portion from the shape of the inner surface contour of the annular bead allows only a portion of the inner region contour of the peripheral rim to contact the inner surface contour of the annular bead when the mounting cup is disposed on the container. The shape of the inner region contour of the peripheral rim is deformed when the mounting cup is crimped to the annular bead of the container. The deformation of the inner region contour reforms the shape of the inner region contour to be substantially the same shape as the inner surface contour of the annular bead to provide a sealing engagement between the mounting cup and the container.
Another modification of the shape and configuration of the mounting cup is described in International Application Number: US88/02489 and corresponding U.S. Ser. No. 312,392. This modification of the mounting cup comprises a non-deformable, annular indent or depression in the curved portion of the channel portion of a gasketed mounting cup. This indent is designed to retain its shape through the clinching process, after which it provides an annular band of enhanced sealing between the mounting cup and the bead of the container.
Despite the attempts to modify the gasket and the mounting cup to improve the reliability of the seal between the channel portion of the mounting cup and the annular bead of the aerosol container, gaskets still become twisted and deformed, particularly during the filling of the container with propellant. The gasket can then be blown into the container or joined to the bead of the container, forming an imperfect seal. Such distortions of the gasket are caused in part by the inherent flexibility of the linear low density polyethylene ("LLDPE") commonly used to form such gaskets. Replacement of LLDPE with high density polyethylene ("HDPE") does not improve the seal. Since the HDPE is rigid, it conforms poorly to the metal of the mounting cup and has insufficient resilience to form a good seal.
The seal between the mounting cup and the aerosol container remains of great concern to both the valve assembly plants and the filling plants since it must be capable of being gas tight for a period of years. In addition, the seal between the mounting cup and the aerosol container must be low in cost to enable aerosol products to be competitive with non-aerosol products in the consumer market.